Metal oxides such as titanium dioxide and zinc oxide are commonly used in several industrial fields. For example, TiO2 is used as an opacifier and/or white pigment in the coatings industry, as filler material in plastics, and as a photocatalyst for removing environmental pollutants. In the coatings industry, TiO2 pigments provide efficient scattering of light to impart brightness and opacity. Titanium dioxide is typically commercially available in the anatase and rutile crystalline forms. Rutile TiO2 is particularly desired because it scatters light more effectively and is more durable than the anatase form.
TiO2 (rutile and anatase) has traditionally been produced by two commercial processes, referred to as the “sulfate process” in which titanium ore is treated with sulfuric acid followed by crystallization and precipitation of TiO2 and the “chloride process” in which titanium ore is treated with chlorine gas to produce an intermediate of TiCl4, which is oxidized to form TiO2. The cost of producing TiO2 from these traditional processes has increased significantly and alternative routes for obtaining TiO2 are being sought.